The present invention relates to a printing device which is able to prevent a printing medium, such as labels, tags, or the like from being thinly, i.e. too tightly or unevenly printed to that averaged clean prints may be attained at all times.
In a hand labeler (i.e., a portable label printing and applying machine), for example, according to the prior art, the inking means for the types has been supplied with an initial ink supply that is gradually used up without being replenished. The time for replacement of the inking means, e.g. an ink roller, has been judged exclusively by the density of the prints upon the labels as seen with the naked eye. More specifically, during the printing operation, the ink roller is replaced with a new one when it is recognized with the unaided eye that the prints on the labels have become thinner than normal. Similar replacements are also performed in other printing devices, such as a table type printer.
However, this aforementioned conventional method for determining the time for ink roller replacement may create a serious defect in the POS (which is the abbreviation of "Point-of-Sale") system which has become widespread in recent years. In the POS system, the information displayed in bar codes, or the like, which are printed on labels, or the like, is read out by means of an optical reader and is then processed by means of a computer. The machine readable prints, such as bar codes, must have far greater clarity than prints that are read out with the naked eye. If the prints should not be clear, they cannot be read out by the optical reader and this would invite serious trouble in the smooth practice of the POS system.